1. Field of the Invention
The present invention relates to an examination method of buffer capacity of saliva, by which the buffer capacity of saliva of a subject can be examined simply without being influenced by the subjectivity of an examiner and to an examination instrument of buffer capacity of saliva, with which the examination method of buffer capacity is suitably carried out.
2. Description of the Conventional Art
The forming and progress of dental caries occur in the following steps. That is, while demineralization wherein acids produced by the metabolism of hydrocarbons by bacteria in an oral cavity elute calcium ions and phosphate ions in teeth, and remineralization that is a phenomenon wherein the calcium ions and phosphate ions are again taken into the teeth, repeatedly act over a long period of time, a balance between the both is broken, and the environment is inclined to the demineralization side over a long period of time, whereby the dental caries is formed and progresses. The role of saliva includes not only a function to supply calcium ions and phosphate ions present in saliva to teeth but also a buffer capacity to neutralize acids produced by the metabolism of hydrocarbons by bacteria in an oral cavity, thereby preventing demineralization. Since there are observed differences in the buffer capacity of saliva against the acids individually, for making a guide for stopping the forming and progress of the dental caries, it is necessary to obtain objective information individually regarding the buffer capacity of saliva.
The buffer capacity of saliva is regulated mainly by the following three buffer functions: a function by the correlation between carbonic acid and a bicarbonate, a function by phosphates, and a function by proteins. Of these, the function by the correlation between carbonic acid and a bicarbonate is the most important, which is based on an equilibrium relation between carbonic acid and the bicarbonate. When an acid is added, the bicarbonate releases carbonic acid as a weak acid. This carbonic acid is rapidly decomposed into water and carbon dioxide, and then is liberated from the solution. In contrast to many buffering agents, this mechanism results in not accumulation of a weak acid but complete elimination of the acid. That is, in order that the buffer capacity of saliva based on the equilibrium relation between carbonic acid and the bicarbonate is maintained, it is considered that a sufficient amount of the bicarbonate for eliminating a large amount of the acid is needed. Further, it is already confirmed that the variation of the bicarbonate in saliva appears in a pH change of saliva.
Accordingly, for examining the buffer capacity of saliva, the evaluation of the amount of the bicarbonate through titration using an acid is the most confident, and its standard method at a laboratory level is the Ericsson's method (see Ericsson Y.; “Clinical investigations of the salivary buffering action”, Acta. Odontol. Scand., 17:131–65 (1959)). This Ericsson's method is a method in which a certain amount of hydrochloric acid is added to collected saliva, the mixture is stirred for a certain period of time while subjecting to a treatment for avoiding bubbling and inclusion of carbon dioxide, and then, the ultimate pH is measured by using electrodes. However, since this method requires a complicated operation and a specific device, it is not generally diffused.
Thus, as a method for examining the buffer capacity of saliva more simply, employed a method in which when saliva is dropped to a paper that has been previously immersed with an acid and a pH indicator and dried, by using a dropping pipette such that the saliva covers the whole of the paper, in the case where the buffer capacity acts against the acid immersed in the paper by the function between the carbonic acid and the bicarbonate in the saliva, and acts until the pH value reaches one exceeding a transition interval of the pH indicator immersed in the paper, the color exhibited by the pH indicator changes, and hence, the pH value of the paper having increased by the buffer capacity of the saliva is determined by comparing a color of the portion to which the saliva has been added with a color sample at a known pH, whereby the buffer capacity of saliva is examined according to three grades of low, medium and high (see Takashi KUMAGAYA, et al., Clinical Cardiology, 130–31, published by Ishiyaku Publishers, Inc.). However, this method involved a problem that since the buffer capacity of the saliva can be evaluated only according to the three grades of low, medium and high, it is not sufficient for more precious examination. Further, this method involved another problem that even a plurality of variations in the colors exhibited by the portion to which the saliva has been added are set up by immersing some kinds of pH indicators in a paper or other means in order to improve the precision of the examination, a scattering in the color determination by an examiner is so large that errors are likely caused.